Abstract: South China Sea Summer Monsoon (SCSSM) is influenced by many factors such as pla teau, ocean (air-sea interaction), cold air, land (land-surface process or land-air interaction) and so on. Indo-China Peninsula，where the earliest Asian summ e r monsoon onset and subtropical high division occur, connects SCSSM to Indian Summer Monsoon and Monsoon of the Bay of Bengal, so the land-surface processes in Indo-China Peninsula is not negligible in SCSSM onset. The cells and precipitation before and after SCSSM onset of 2004 were analyzed to study the activity feat ures of SCSSM, and then the effects of the land-surface processes in Indo China Peninsula on the SCSSM onset and intensity were explored. The SCSSM of 2004 broke out on 19th May, which is analyzed by NCEP reanalysis data and precipitation observations of stations. The results indicate that strong convection activity drifts from Bay of Bengal to Indo-China Peninsula,and enhanced precipitations in Indo-China Peninsula change the land-surface process. So, the anomalies occur on the air temperature difference between Indo-China Peninsula and South China Sea in the lower troposphere and play an important role on the SCSSM onset. Moreove r, the anomalies of the air temperature difference between Indo-China Peninsula and South China Sea in the lower troposphere relate closely to the activities of SCSSM. Usually, active and non-active SCSSM accompany by the negative anomalies,and SCSSM break soon after the positive anomalies occur.